feat: add uv / PEP 723 support

[al-bashkir]

Adds uv / PEP 723 inline script metadata support so users can run the plugin without manually installing libtmux. Existing
python3 + system libtmux path is unchanged.

What changes

• scripts/rename_session_windows.py — PEP 723 metadata block added after the shebang. The block is a Python comment so the file still runs as-is under python3; uv parses it and provisions a cached venv
  with libtmux.
• tmux_window_name.tmux — auto-detects uv on PATH. If found, all script invocations route through uv run --script. Otherwise the original python3 + libtmux import check runs unchanged. Zero config;
  existing users see no behavior change.
• enable_user_rename_hook — the after-rename-window hook value previously hardcoded the bare script path and relied on the python3 shebang. That bypassed the launcher under the uv path. Now it reads
  TMUX_WINDOW_NAME_LAUNCHER (exported from .tmux) and prefixes the hook's run-shell command. Pre-existing unbalanced quotes around the run-shell argument are also fixed (they broke once the path string
  contained spaces from the uv run --script prefix).
• README.md —
  • New ### Recommended: install uv section above the libtmux install instructions, explaining pip install is not needed when uv is present.
  • The nvim Lua autocmd, vim job_start, and zsh chpwd snippets gain parallel uv run --script variants below the originals (originals kept as-is).

How to verify

# uv path — works without system libtmux
uv run --script scripts/rename_session_windows.py --help

# python3 path — works with system libtmux installed (existing behaviour)
python3 scripts/rename_session_windows.py --help

Manual smoke (4 quadrants):

┌────────────┬────────────────┬──────────────────────────────────────────────┐
│ uv on PATH │ system libtmux │                   Expected                   │
├────────────┼────────────────┼──────────────────────────────────────────────┤
│ yes        │ no             │ hooks register with uv run --script prefix   │
├────────────┼────────────────┼──────────────────────────────────────────────┤
│ yes        │ yes            │ uv branch wins (prefix in hook value)        │
├────────────┼────────────────┼──────────────────────────────────────────────┤
│ no         │ yes            │ original python3 branch, no behaviour change │
├────────────┼────────────────┼──────────────────────────────────────────────┤
│ no         │ no             │ existing tmux error display, plugin disabled │
└────────────┴────────────────┴──────────────────────────────────────────────┘

Verify hook strings:
tmux show-hooks -g | grep 8921

Notes

- requires-python = ">=3.7" matches the existing pyproject.toml ruff target-version.
- No automated test changes. Existing pytest suite continues to use system-installed libtmux.
- path_utils.py is unchanged — PEP 723 metadata only goes on the entrypoint script.